The present invention relates to a zoom lens unit being small in size and having shock resistance, as well as to an image pickup device using the same.
Conventionally, for zoom lenses as an example, there have been proposed various types of lens driving units for driving two or more lens groups along an optical axis direction. FIG. 9 is a perspective view of a zoom lens unit disclosed in JP 2005-77714 A as an example of the lens driving unit. It is noted that in the future, a Z direction is headed toward an image pickup element side, while a −Z direction is headed toward a subject side.
The zoom lens unit shown in FIG. 9 has a first lens holder 3 for holding a first lens group 1 and a second lens holder 4 for holding a second lens group 2, where the first lens holder 3 is composed of a first frame 5 and a second frame 6. The first frame 5 of the first lens holder 3 and the second lens holder 4 are guided in an optical axis direction (Z direction) by a first guide shaft 7. Also, the second frame 6 of the first lens holder 3 and the second lens holder 4 are guided in the optical axis direction by a second guide shaft 8. In this way, the first lens holder 3 and the second lens holder 4 can be moved in the optical axis direction along the two guide shafts 7, 8.
The second frame 6 of the first lens holder 3 and the second lens holder 4 can be moved in the optical axis direction along a recess of a cam 9, in which the recess is formed along the rotational direction of the cam (not shown). In this connection, the first lens holder 3 and the second lens holder 4 are biased in mutually approaching directions by a bias spring 10 so as to be connected to each other. Then, the first lens holder 3 and the second lens holder 4, which are brought into close contact with the recess of the cam 9 by the biasing force of the bias spring 10, and driven in the optical axis direction by rotation of the cam 9.
However, the conventional zoom lens unit disclosed in JP 2005-77714 A has problems as shown below.
That is, the bias spring 10 provided for bringing the first lens holder 3 and the second lens holder 4 into close contact with the recess of the cam 9 is fitted to side faces of the first lens holder 3 and the second lens holder 4.
Nowadays, there is a growing trend that the zoom lens unit is mounted even on small-size terminal equipment, and the lens and the holder are going smaller in size and thinner in the thickness in the optical axis direction. Besides, those are formed from resin for easiness of configurational fabrication. Accordingly, in the case where the bias spring 10 is fitted to the side faces of the lens holders 3, 4 as in the conventional zoom lens unit, the lens holders 3, 4 are pressed against the guide shafts 7, 8 by the bias spring 10, so that the guide shafts 7, 8 serve as a restraining part to cause the lens holders 3, 4 to be flexed in the optical axis direction, giving influences on the optical characteristics, disadvantageously.
It would be possible to form the first lens holder 3 and the second lens holder 4 into a configuration with considerations given to the occurrence of the flexure. However, if the two lens holders 3, 4 are held in a normally loaded state, there would occur creeps or plastic deformation to the resin from which the lens holders 3, 4 are made, causing performance deteriorations as another problem.
Further, fitting the above-described bias spring to the small lens holders in small-size equipment would cause the assemblability to degrade. Moreover, for small-size equipment, it is impossible to allow a large space for the fitting of the bias spring to the two lens holders, so that the fitting portion of the bias spring cannot be made strong. As a result, there is another problem that the bias spring is more liable to fall off upon application of an impact.